Dunnett Method

mice example

Setup

Assume data are in C2 (score) and groupings in C1 (group). Do StatANOVAGeneral Linear Model.

Then click `Comparisons`
and click `Factor Plots`

Session Output

```General Linear Model: score versus group

Factor  Type   Levels  Values
group   fixed       3  1, 2, C

Analysis of Variance for score, using Adjusted SS for Tests

group    2   673.00   673.00  336.50  4.55  0.029
Error   15  1109.50  1109.50   73.97
Total   17  1782.50

S = 8.60039   R-Sq = 37.76%   R-Sq(adj) = 29.46%

Unusual Observations for score

Obs    score      Fit  SE Fit  Residual  St Resid
2  32.0000  52.8333  3.5111  -20.8333     -2.65 R

R denotes an observation with a large standardized residual.

Bonferroni 95.0% Simultaneous Confidence Intervals
Response Variable score
Comparisons with Control Level
group = C  subtracted from:
|
group   Lower  Center  Upper  --+---------+---------+---------+----
1       2.137   14.50  26.86    |  (--------------*---------------)
2      -1.863   10.50  22.86  (-+------------*---------------)
--+---------+---------+---------+----
0.0       8.0      16.0      24.0

Bonferroni Simultaneous Tests
Response Variable score
Comparisons with Control Level
group = C  subtracted from:

group    of Means  Difference  T-Value   P-Value
1           14.50       4.965    2.920    0.0211 *
2           10.50       4.965    2.115    0.1032

Dunnett 95.0% Simultaneous Confidence Intervals
Response Variable score
Comparisons with Control Level
group = C  subtracted from:
|
group   Lower  Center  Upper  --+---------+---------+---------+----
1       2.388   14.50  26.61    |  (--------------*--------------)
2      -1.612   10.50  22.61  (-+------------*--------------)
--+---------+---------+---------+----
0.0       8.0      16.0      24.0

Dunnett Simultaneous Tests
Response Variable score
Comparisons with Control Level
group = C  subtracted from:

group    of Means  Difference  T-Value   P-Value
1           14.50       4.965    2.920    0.0195 *
2           10.50       4.965    2.115    0.0916

```

Both methods consistently imply that group 1 mean differs from the control group mean while group 2 mean does not.

The Dunnett's intervals are tighter than the respective Bonferroni's counterparts.

Main Effect Plot -- mice example

Group 1 mean differs apparently from control group mean. It's less certain from the graph whether group 2 mean differs from control group mean.